ALP
What it measures, and what changes the number.
ALP (alkaline phosphatase) is an enzyme found in several tissues, mainly the liver and bile ducts and the bones, with smaller amounts from the intestine and, during pregnancy, the placenta. The blood test measures total ALP activity from all these sources combined.
It is usually part of a liver panel with ALT, AST, GGT and bilirubin. GGT is especially useful alongside it because it rises with bile duct activity but not with bone activity, which helps suggest where the ALP is coming from. Calcium and other bone markers may be read with it for the same reason.
Results are read in the context of age, because growing children and adolescents have more bone-derived ALP, and in pregnancy. A fatty meal can add intestinal ALP in some people, so fasting samples are sometimes preferred. Blood drawn into EDTA tubes can give falsely low activity. Reports may list it as Alkaline Phosphatase (ALP) or Fosfatasa alcalina (ALP).
Often read alongside: GGT, ALT, AST, Bilirubin (total), Calcium (total)